U.S. Pat. No. 4,952,556, Mantese et al. discloses a method for making patterned films of superconductor materials. The method involves depositing films of a metallo organic material on a substrate and patterning the film with an electron beam, ion beam or laser. The patterning is accomplished by local heating or energy deposit in the film and does not involve a photochemical reaction.
Various electronic devices can be made by depositing thin patterned films of materials having different electrical characteristics on a substrate. Current techniques for manufacturing such devices generally begin with a suitable substrate, such as a wafer of crystalline silicon, on which materials having various electrical characteristics are deposited. These current techniques are expensive because they generally include many steps. Typically, each step involves applying a photo-resist to the surface of the substrate; changing the properties of selected areas of the photoresist by exposing those areas to light, X-rays or an electron beam; removing either the exposed or unexposed portions of the photoresist to expose portions of the underlying substrate; chemically treating or depositing a material on the exposed portions of the substrate; and removing the photo-resist. A disadvantage of many such prior art techniques is that resolution can be lost in what is essentially a two-stage masking process.
Some prior art processes include depositing a layer of material on a substrate, applying a photoresist to areas where it is desirable to retain the material, and then etching the material away in places where it is not required. This method has the disadvantages set out above and the further disadvantage that the edges of the retained material can be rough or undercut. This can ultimately lead to cracks which can cause the device to fail.
Another disadvantage of these processes is that they tend to produce a non-planar surface. In these methods materials are often not uniformly deposited over the surface of the substrate. If a generally planar surface is required then a separate planarization step is required.
In many instances it is necessary to apply a metal film to a semiconductor material to make or connect to an electronic device. Prior art techniques apply such films by evaporation. Evaporation heats the material to which the film is being applied. The high temperature produced at the interface between the evaporated metal and the underlying material causes metal atoms to diffuse into the material and vice-versa. This results in a layer of mixed metal and semiconductor at the metal-semiconductor interface which can interfere with the performance of the device.
Japanese patent application No. 1004738, assigned to Fujitsu Ltd., discloses a method for making a patterned film on a substrate. The method involves depositing a metallic resinate, together with a photo-crosslinking agent, on a substrate. The photo-crosslinking agent is then exposed and developed to yield a pattern which can be reduced to a pattern of metallic wires by sintering. This method does not disclose a photochemical reaction which causes a metal complex to convert into a metal containing material, such as metal oxide, on a substrate. It requires a high temperature sintering step which is not necessary in processes according to the present invention.
Japanese patent application No. 62263973, Omura, discloses a method for making a patterned thin metal film. The method uses an electron beam to decompose portions of an organometallic thin film to form metals. This method does not involve a photochemical reaction.
Kestenbaum et al., U.S. Pat. No. 5,064,685, discloses a method for making patterns of metals. The method involves applying a metal-organic ink to a substrate. The metal organic ink is then heated with a laser to pyrolize the ink to leave a deposited metal film. This method exposes the substrate to high temperatures and does not allow for the deposition of materials other than metals.
Bickley, et al. Solid state photochemistry of (C.sub.8 H.sub.12)Pt(N.sub.3).sub.2 as thin films on Si(111) surfaces J. Photochem. Photobiol. A: Chem., 67 (1992) 181-186 and Ho et al. Solid state photochemistry of (C.sub.2 H.sub.4 (Ph.sub.2 P).sub.2)M(N.sub.3).sub.2 (M.dbd.Ni, Pd, Pt) on Si(111) surfaces J. Photochem. Photobiol. A: Chem., 69 (1992) 229-235 disclose that certain metal complexes deposited on a Silicon substrate can be caused to undergo photochemical reactions which result in the loss of the ligands associated with the metal complex. The films of metal which were produced were very impure. These references do not disclose or suggest direct patterning of amorphous films of metal complexes. They suggest that such metal complexes might be useful in photochemical vapour deposition.
Some researchers have experimented with photolithography of metal containing polymer films to produce patterns of metals. These methods generally involve patterning a photosensitive polymer film, washing away some parts of the film with a solvent and then reducing the remaining parts of the film to a metal film by pyrolysis. It is hard to produce pure metal films by these techniques.